Concrete is often cast in place, for example, by pouring wet concrete over a surface and allowing it to cure to form slabs. For logistical and technical reasons, concrete slabs for example, utilized for flooring, paving, and transportation are often made up of a series of individual blocks. Referring to FIG. 1, a concrete product, such as concrete floor 100 is typically made up of a series of individual blocks or slabs 102-1 through 102-6 (collectively 102). The same is true for sidewalks, driveways, roads, and the like. Blocks 102 provide several advantages, including relief of internal stress due to drying shrinkage and thermal movement.
Adjacent blocks 102 meet each other at joints, such as joints 104-1 through 104-7 (collectively 104). There may be different types of joints, for example, the term “construction joint” is often used to define a termination point that separates an initial pour from a second pour, such as a first day's pour from a second day's pour. Other joints may be created within large slabs or blocks. For example, the term “contraction joints” often is used to refer to joints intentionally created that allow for at least the partial relief of internal stresses in the concrete slab that build up due to thermal expansion or drying shrinkage. Regardless, joints 104 are typically spaced so that each block 102 has enough strength to overcome internal stresses that would otherwise cause random stress relief cracks. In practice, blocks 102 should be allowed to move individually but should also be able to transfer loads from one block to another block.
Transferring loads between blocks 102 is usually accomplished through dowels, which historically have been smooth steel rods embedded in the two blocks 102 defining the joint 104. For instance, FIG. 2 shows a side view of dowel 200 between slabs 102-4 and 102-5 and FIG. 3 is a cross-sectional plan view along a section a portion of which is depicted by sectional arrow 3-3 in FIG. 2. FIG. 3 shows several dowels 200 spanning joints 104 between slabs 102. Such circular or square dowels are capable of transferring loads between adjacent slabs 102, but have several shortcomings. One is that dowels 200 are typically used to prevent relative vertical movement between adjacent slabs. While this property is beneficial after curing, it is detrimental during the curing process. Freshly placed concrete, which includes cement and water, shrinks considerably as it hardens due to the chemical reactions between the cement and the water, i.e., hydration.
Other internal stresses in concrete slabs result from the differences in temperature, humidity and available water between various portions, such as the top and the bottom, of a slab during curing. For example, FIG. 4 shows a side view of slab 402 (having a top 404, bottom 406 and edge 408) and slab 410 (having top 412, bottom 414 and edge 416), which are undergoing a curing process. Due to differences in temperature, humidity and/or available water between the tops 404, 412 and the bottoms 406, 414 of the slabs 402 and 410, the edges 408, 416 may move vertically along axis 418. For example, slabs 402 and 410 are shown moving vertically (or “curling”) away from surface 420. While the edges 408, 416 of slabs 402, 410 are shown moving away from surface 420 to form a concave top surface, the conditions may result in the edges 408, 416 of one or more of the slabs 402, 410 moving downwards towards surface 420 to form a slightly convex upper surface (“warping”). Regardless of the direction of the movement along axis 418, the interface between the two adjacent slabs 402, 410 is often altered.
As discussed above, conventional dowels are rigid structures, thus they do not accommodate the relative curling or warping movement at the periphery of a slab, nor compensate for the curling or warping movement of the periphery of the adjacent slab. For example, FIG. 5 shows a side view of slab 502 (having a top 504, bottom 506 and edge 508) and slab 510 (having a top 512 and a bottom 514). During curing, variations in temperature, humidity and/or available water between the tops 504, 512 and the bottoms 506, 514 of the slabs 502 and 510, may lead to curling and/or warping. As shown in FIG. 5, the edges 508, 516 may move vertically along axis 518. For example, slabs 502 and 510 are shown moving vertically upwards (curling) away from surface 520.
Dowel 522 is a rigid structure that extends across joint 524 and is embedded within slabs 502, 510. Being rigid, dowel 522 may undesirably restrict slabs 502, 510 from moving relative to each other along the vertical axis 518 of joint 524 during curing, thereby resulting in stresses that can accumulate and lead to failure of the concrete around the dowel or cracking in the slabs as shown by cracks 526, 528. Thus, the art would benefit from an improved dowel and methods of using an improved dowel that overcomes one or more of the shortcoming of prior art systems and methods.